Advisory Council on the Environment

Environmental Impact Assessment Ordinance (Cap. 499)

(ACE-EIA Paper 18/2002)
For Advice

Environmental Impact AssessmentConstruction of Lung Kwu Chau Jetty

Purpose

This paper presents the key findings and recommendations of the Environmental Impact Assessment (EIA) Report for the Construction of Lung Kwu Chau Jetty (hereafter known as the Project), submitted under section 6(2) of the Environmental Impact Assessment Ordinance (EIAO). The Civil Engineering Department (CED) and their consultants will make a presentation. Comments from the public and ACE will be taken into account by the Director of Environmental Protection when he makes his decision on the approval of EIA report under the EIAO.

Advice Sought

2. Members' views are sought on the findings and recommendations of the EIA report.

Need for the Project

3. A Doppler VHF Omni-directional Range and Distance Measuring Equipment (DVOR/DME) Station is being operated on Lung Kwu Chau to provide bearing and distance information to the approaching/departing aircrafts to/from the Chek Lap Kok Airport. According to Civil Aviation Department (CAD), the existing jetty at Lung Kwu Chau, which is ruined and abandoned for use, is too small and of too shallow water depth to accommodate the CAD's vessels for transporting equipment and personnel for servicing and maintaining the DVOR/DME. Currently, the transportation has to rely on helicopters, which is however prohibited during night times and adverse weather conditions. In order to allow emergency repair work be carried out during such periods as to maintain normal air traffic control and flight safety, CAD has proposed to construct a proper jetty for berthing of marine vessels.

Description of the Project

4. The Project is to construct a jetty at Lung Kwu Chau as shown in Figure 1. The jetty will consist of a 10m by 20m single berth jetty head and a 5m by 22m long catwalk constructed from pre-cast structure. The Project will involve dredging of an approach channel of 1,978 m2 to a level of -2.5mCD and will generate 5,550 m3 of uncontaminated dredged sediment. Maintenance dredging of the approach channel will be carried out every five years. The existing jetty will be demolished after completion of the new jetty.

5. As the work site of the Project falls wholly within the Sha Chau and Lung Kwu Chau Marine Park and the Site of Special Scientific Interest at Lung Kwu Chau, Tree Island and Sha Chau, the Project is a Designated Project under section Q.1, Part I of Schedule 2 of the EIAO.

Consideration of Alternative Jetty Locations and Design Options

6. Alternative locations at Lung Kwu Chau for the jetty and alternative design options for the construction of the jetty have been considered in the EIA study with a view to minimizing the environmental impacts arising from the project and shortening the construction period.

7. The preferred location of the jetty as shown in Figure 1, will achieve better environmental performance than the original location as shown in Figure 2 because of reduction to catwalk length from 62m to 22 m, reduction to approaching channel area from 8,300 m2 to 1,978 m2 and reduction to volume of dredged sediment from 14,300 m3 to 5,550 m3.

8. The preferred design of the jetty has adopted a blockwork structure with pre-cast concrete block used for the construction of the jetty head and catwalk adopted. The preferred design option will eliminate the need for any piling works which would be the most significant potential source of impact on Chinese White Dolphins. Furthermore, there will be large diameter openings along the bottom of the catwalk to facilitate seawater circulation.

Specific Environmental Aspects to Highlight

9. The key environmental issues identified for this project are water quality impact and ecological impact.

Water Quality Impact

10. The Project will have the potential to cause water quality impact during the dredging of 5,550m3 of uncontaminated sediment. The numerical modelling carried out for water quality assessment indicated that in view of the short duration of the dredging period of about 14 days and small dredging rate of 500 m3 per day, with the implementation of mitigation measures including the use of silt curtain and closed grab dredger, the dredging would unlikely cause unacceptable impact.

11. The assessment has also considered the worst case scenario when the ambient suspended sediment levels in the water measured during the 4-weeks baseline monitoring programme carried out prior to the Project is lower than that assumed in the assessment. Under the situation, additional measures including the deployment of double silt curtain and reduction of dredging rate by 50% will be implemented to avoid adverse water quality impact.

Ecological Impact

12. The report predicted that 0.008 ha of backshore vegetation habitat, 0.002 ha of intertidal habitat and 0.23 ha of subtidal habitat would be lost due to the construction of footpath. The overall impact is acceptable as species diversity at the habitats is low and no rare species was identified during the ecological survey.

13. Although the dredging will have the potential to increase siltation, the report predicted that with the implementation of water quality mitigation measures including the use of silt curtains and closed grab for dredging, the effects of increases in siltation due to dredging on nearby marine habitat within the Sha Chau & Lung Kwu Chau Marine Park can be controlled to an acceptable level.

14. Since the Project site is located within the Marine Park, a package of measures for the protection of Chinese white dolphin would be implemented. The measures include prohibiting underwater blasting work, limiting the speed of vessel to 10 knots within the Marine Park and to avoid dredging works during the period of peak dolphin abundance in North Lantau waters. Furthermore, an exclusion zone of 500m radius will be established at the works site which will be scanned for at least 30 minutes prior to the start of dredging. If dolphins are observed in the exclusion zone, marine works should be delayed until the dolphins have left the area. If dolphins enter the exclusion zone after dredging has commenced, marine works should cease until they have left the area.

Environmental Monitoring and Audit (EM&A)

15. An EM&A programme has been proposed in the EM&A Manual submitted together with the EIA report and included a detailed Implementation Schedule. The EM&A requirements will be enforced as Environmental Permit conditions.

Public Consultation

16. CED is going to exhibit the EIA report, EM&A manual and Executive Summary available for the public to comment under the EIAO on 24 September 2002. Members will be briefed at the meeting about any comments received from the public.